Effect of Quaternization on Structure and Adsorptivity of Hyper Cross-Linked Poly(vinyl imidazole) for Thiohenic Sulfurs in Model Oil

A hyper cross-linked polymer, HCPVIM, was prepared by copolymerization of vinylimidazole (VIM) and divinylbenzene (DVB), whereby three poly ionic liquids (PILs) were synthesized via quaternization of the imidazole ring by hydrochloric acid, n-butyl chloride and 1,4-bis(chloromethyl) benzene, respectively. Their composition, morphology, specific area and thermal stability were characterized, and their adsorptivity for thiophenic sulfurs was studied. The HCPVIM is a mesoporous sorbent with specific area of 675 m2 g–1, and shows much higher desulfurization ability than its monomer analogue, ethyl imidazole, being about 8.0 mg S g–1 for dibenzothiophene (DBT) at equilibrium S-concentration of 900 ppm. Its desulfurization ability follows the order of DBT > benzothiophene> thiophene, being the same order as alkyl imidazole and imidazolium based ionic liquids. Compared to HCPVIM, the PILs are also mesoporous materials but with negligible micropores, lower specific area of ∼180 m2 g–1, and lowering thermal decomposition temperature of about 150 K. The PILs show a complex adsorption behavior for different sulfur compounds. As a whole, quaternization of HCPVIM tends to decrease the desulfurization ability for all sulfur compounds except the protonated HCPVIM for thiophene, which manifests the combinative effects of the decreased porosity and specific area and the increased electrostatic interactions in the ionized sorbents.